System of electrical distribution.



R. O. HULL.

SYSTEM OF ELECTRICAL DISTRIBUTION.

APPLICATION FILED MAR.18, 1910.

1,014,395. v Patented Jan.9, 1912. I

2 SHEETSSHBET 1.

cp 0 m lwmmo'r SYSTEM OF ELEU'I'EIUALI ulfil'runullun. APPLICATION FILED MAR.18,1910.

1,014,395. Patented Jan.9,1912.

2 SHEETSSHEET 2.

U IT D STATES PATENT oFFIo ROBERT o. HULL, or PHILADELPHIA, PENNSYLVANIA. H

SYSTEM or ELECTRICAL DISTRIBUTION.

Specification of Letters Iatent.

Application filed March 18, 1910. Serial'No. 550,163.

Patented Jan. 9,1912.

Y To all whom it may concern:

Be it known that I, ROBERT C. HULL, a

, citizen of the United States, and residing in the city of Philadelphia, State of Pennsylvania, have invented certain new and useful Improvements in Systems of Electrical Distribution, of which the. following is a specification.

My invention relates to those systems of distribution in which a dynamo electric machine is driven at a variable speed, as for example, by the axle of a moving vehicle or by a windmill, and supplies current to translating devices requiring a constant potential.

My invention applies more especially to systems such as described in patent application #507,316 filed July 13th, 1909 by J. Lester Woodbridge and myself jointly, and comprises improvements in the means for providing the primary excitation for the generator fields whereby .the construction and windings on these fields is made less expensive. In the application cited above, the primary excitation is produced by two .opposing field windings, one of which. is supplied with a substantially constant ourrent while the current in the other varies with the voltage of the circuit to be regillated. The primary excitation is the resultant of the difference between these two windings and is a small percentage of the effect which either one alone will produce. It is, therefore, necessary to provide a considerable excess of field winding above that actually necessary to produce the primary excitation. In the present invention, I provide means whereby this excess of field winding is obviated, a single winding only being required for the primary excitation, the current in which is reduced to zero by a special arrangement of circuits and devices when the voltage on the work circuit reaches its limiting value. This latter voltage can, therefore, never reach this limiting value. a

In the accompanying drawings, Figurel shows one embodiment of my invention ap-' plied to a generator of the three pole type, while Fig. 2 shows the same arrangement applied to another type of generator, and Fig. 3 shows the same arrangement applied to the exciter of a standard generator.

Referring to Fig. 1, A is the armature and B the commutator of a enerator whose field frame is shown at C, t is latter poles.

"potential between the brushes 7-8.

being provided with three internally projecting poles, D, E and F. The armature is driven at a variable speed by belting its pulley I to the axle J 0t a moving vehicle, such as a railway car. Three brushes 78 9 bear upon the commutatorB at equidistant points, and the armature is so wound that the potential between each pair of brushes is fixed by the algebraic sum of the mag netic flux in the corresponding pair of The construction of such a machine is fully described in Patent No. 895824 to J. L. Woodbridge, August 11th, 1908. The primary excitation of this machine is produced by the field winding 1314 on the poles E and D respectively. This winding produces a flux in the direction of the arrow M. This flux produces a difference of The secondary excitation is produced by field windings 10 11-42, which are connected in series across the brushes 7-8. These windings produce a flux in the direct-ion of the arrows N N. This fiux will produce a voltage between the brushes 8 and 9, and the same voltage between the brushes 7 and 9. So far as the flux represented by the arrows N N is concerned there will be no difierence in voltage between the brushes 7 and 8, whatever difference exists between these brushes being produced by the flux represented by the arrow M. The brush 9 constitutes one of the main terminals of the machine while a point 19 in the field circuit 101112 midway between the brushes 7 and 8 constitutes the other main terminal. of the machine. These two terminals are connected to the circuit 12 which supplies the load L. The primary windings 1314 are connected to the point-s 17 and 18 of a \Vheatstone bridge, the other junction points of the bridge 15, 16 being connected respectively tothe conductors 1, 2. The Wheatstone bridge comprises two resistances, 5 and 6, having a practically zero temperature coeiiicient, located in two opposing legs and two high temperature co-efficient resistances, 3 and 4 located in the other two opposite legs. These last two resistances may be of the well known hot iron wire type whose resistance increasesvery rapidly with very small increments of current between certain limits so that over a considerable range of applied voltage across their terminals the flow of current remains substantially constant. The volt- 'mum and the limiting value.

age at which these are most sensitive should be chosen atabout half of the voltage desired across the circuit 1-2. If, new the resistances 5 and 6 be so designed that with a current flowing through them equivalent'to the constant current for which the resistances 3 and 4 are designed, the drop in voltage across the resistances 5 and 6 will be just half of the desired limiting voltage across the circuit 1-2, then at this limiting voltage there will be no difi'erence of potential between the points 17 and 18 and no current will flow through the primary field winding 13 and 14. It is evident that under these conditions the. voltage across the circuit 1-2 can never quite reach the sufiicient excitation to maintainthis slightly reduced voltage at the lowest desired speed of the axle J. For all speeds above this the voltage will have a value between this mini- The difi'erence between these two limits may bemade so small as to be negligible, and the machine will have a practically constant voltage for all speeds above the critical speed selected as a minimum.

The combination shown in F ig. 2 includes the same arrangement of VVheatstone bridge but a different type of generator. This generator comprises an armature A having a commutator B rotating in the field .frame C which is provided with two internally projecting poles of peculiar shape arranged to provide for two sets of magnetic lines. One of these represented by the arrows M is produced by the primary excitation due to the windings 24 and 25 wound on the neck of each pole piece. These windings are connected across the points 17 and 18 of the -W'heatstone bridge as in Fig. 1. Two pair of brushes bear on the commutator B of which one pair 22 and 23 are located at points of potential difference due to the flux M These brushes are short-circuited. A small amount of flux in the direction of the arrows M will produce a considerable flow of current through the short-circuit, thereby giving rise to a magneto-motive force in the armature winding which will produce the secondary flux represented by the arrows N the other pair of brushes 20 and 21 which are connected to the circuit l2.

As described in connection with Fig. 1

there will be a certain limiting voltage across the circuit 1.2 at which the VJheatstone bridge will be exactly balanced and there will be no flow of current through the windings 2425, so that the voltage across the circuit 12 can never quite reach this limit. In Fig. 3 the same arrangement of Wheatstone bridge is shown, to which is connected the field winding 31 of an exciter O mounted on the shaft of the armature A of the generator. The exciter supplies current to the field windings 32 and 33 of the generator in the usual manner. As explained in connection with the previous figures there will be a voltage across the circuit 12 at which the Wheatstone bridge will be exactly balanced and no current will flow through the field winding 31 of the exciter, while with a voltage slightly below this limit a sufl'icient flow of current will pass through the winding 31 to develop a voltage in the exciter 0 suitable for exciting the windings 32 and 33 of the main machine to maintain the said voltage across the circuit 1-2 at the minimum speed of operation.

What I claim and desire to secure by Letters Patent is,

In combination, a dynamo electric ma chine having an armature and its commufor two sets of magnetic lines, constituting a primary and a secondary magnetic flux displaced from each other whereof the path for the primary flux is in part distinct from the path for the secondary flux, one pair of brushes bearing upon the armature at points of potential difference due to the primary flux, a conducting circuit of low resistance connecting said brushes, a second pair of brushes bearing upon the armature at points of potential difference due to the secondary flux, a consumption circuit connected to said second pair of brushes, a Nheatstone bridge including resistances having different temperature coeflicients, connections from two opposite junction points of said bridge to the consumption circuit, and a field winding on that part of the path for the primary flux whichis distinct from the other path, said winding connected across the other two opposite junction points of the bridge.

In testimony whereof, I have hereunto signed my name.

ROBERT C. HULL.

, WVitnesses:

J. LESTER WooDBRmeE, J OSEPH H. TRACY.

'tator and a field structure providing paths 

